Mal Priyanath, Bera G, Turpu G R, Srivastava Sunil K, Gangan A, Chakraborty Brahmananda, Das Bipul, Das Pradip
Department of Pure and Applied Physics, Guru Ghasidas Vishwavidyalaya, Koni, Bilaspur-495009, India.
Department of Physics, Mahatma Gandhi Central University, East Champaran, Motihari, Bihar-845401, India.
Phys Chem Chem Phys. 2019 Jul 10;21(27):15030-15039. doi: 10.1039/c9cp01494b.
Herein, using Raman spectroscopy, we have presented the investigation of a temperature-dependent frequency shift and the line broadening of phonon modes by inserting the atomic layers of Pb and PbTe in the prototype 3D topological insulator Bi2Te3. Good quality single crystals of Pb2Bi2Te3, PbBi2Te4, and PbBi4Te7 were grown using the modified Bridgman technique. The Raman modes show progressive blue-shift with the decrease in temperature from 298 K to 93 K in Pb2Bi2Te3, PbBi2Te4, and PbBi4Te7 due to the anharmonic vibrations of the lattice as well as the increase in the strength of Bi-Te covalent interactions. The experimental results were complemented by extensive first principles calculations, where a reasonable matching between the experimental and computational data was found. Chemical pressure, induced by the insertion of Pb and PbTe layers in Bi2Te3, modified the interactions at the boundaries of the quintuple-layers, which was evident from the evolution of the A21u mode. The enhancement in the out-of-plane Bi-Te vibrations with respect to the in-plane Bi-Te vibrations was observed at low temperatures. The temperature coefficients of the Raman modes were useful in determining the thermal conductivity, which is a key design parameter for the fabrication of spintronic devices using topological insulators. The estimated first order temperature coefficient (χ') for Pb2Bi2Te3 signified the decrease in the thermal conductivity relative to Bi2Te3, which was caused by the insertion of the Pb layers in the van der Waals gaps of Bi2Te3.
在此，我们利用拉曼光谱法，通过在典型的三维拓扑绝缘体Bi2Te3中插入Pb和PbTe原子层，对声子模式的温度依赖性频移和线宽展进行了研究。采用改进的布里奇曼技术生长出了高质量的Pb2Bi2Te3、PbBi2Te4和PbBi4Te7单晶。在Pb2Bi2Te3、PbBi2Te4和PbBi4Te7中，由于晶格的非谐振动以及Bi-Te共价相互作用强度的增加，拉曼模式在温度从298 K降至93 K时呈现出逐渐的蓝移。大量的第一性原理计算对实验结果进行了补充，实验数据与计算数据之间存在合理的匹配。在Bi2Te3中插入Pb和PbTe层所引起的化学压力改变了五重层边界处的相互作用，这从A21u模式的演变中可以明显看出。在低温下观察到面外Bi-Te振动相对于面内Bi-Te振动有所增强。拉曼模式的温度系数有助于确定热导率，热导率是使用拓扑绝缘体制造自旋电子器件的关键设计参数。Pb2Bi2Te3的一阶温度系数（χ'）估计值表明其热导率相对于Bi2Te3有所降低，这是由于在Bi2Te3的范德华间隙中插入了Pb层所致。
